The present invention relates, in general, to a drive system, and more particularly to a drive system of a type including a motor, a converter with a voltage intermediate circuit, and a holding brake, whereby the holding brake is mechanically connected to the motor and the converter is electrically connected to the motor.
Drive systems of this type are employed in applications when the motor is at a standstill and has to be held in this stop position. Applications that require such drive systems, include, for example, elevators or cranes.
It is generally known to equip the holding brake for actuation with a contactor, an external DC supply, and a brake control unit. The external DC supply is electrically connected in parallel to terminals of the holding brake, whereby the contactor is positioned in one such connection. The contactor is controlled by the brake control unit, which receives a brake signal from a primary control device. Such a conventional drive system suffers shortcomings because of the need for external wiring and the incorporation of a contactor. As the contactor delay time is unknown, also the brake switching delay time is unknown. This leads to problems as far as projecting the delay time between the brake control and control of the converter, which powers the motor, is concerned. Thus, as soon as the motor is held in stop position by the holding brake, there is no need to supply the motor via the converter with electric energy so that the pulses of the converter are blocked.
Attempts were made to address the problem of unknown delay times by assigning the control of the holding brake to the converter rather than to the brake control unit. As a consequence, dead times are omitted between the command of a brake control unit and the enablement of the internal pulse of the converter which now regulates by itself the time behavior of the brake control and the pulse enablement. Moreover, the holding brake includes a contactor and an external DC supply, which have to be wired together.
It would therefore be desirable and advantageous to provide an improved drive system to obviate prior art shortcomings.